1. Field of the Invention
The present invention relates to a method and apparatus for decomposing organic fats and oils containing PCB (polychloro biphenyl) and for making them innoxious, and more particularly to a PCB decomposing method and apparatus in which PCB is mixed with water, an oxidizing agent and sodium carbonate, and decomposed under pressure at an elevated temperature.
2. Description of Related Art
Conventionally, several PCB decomposing methods have been known and their practical use has been studied by electric power companies, various manufactures and the like. However, only a few PCB decomposing methods have been completed and put to use for actual PCB decomposition treatments.
FIG. 10 shows a structure of a conventional PCB decomposing apparatus. In this PCB decomposing apparatus, a material to be treated which is contained in a transformer or the like is put in PCB extracting container 1. An organic solvent is fed from distilling tower 2 into the PCB extracting container 1 through transfer pump 4, and PCB is extracted with the organic solvent. The PCB extracted in the PCB extracting container 1 and the organic solvent are fed to the distilling column 2 through the transfer pump 3. In the distilling column 2, the organic solvent is distilled to separate the PCB. Then, the PCB circulates into the PCB extracting container 1 through the transfer pump 4.
The PCB extracted in the distilling tower 2 is mixed with water 10, aqueous hydrogen peroxide 11 and aqueous Na.sub.2 CO.sub.3 solution 12. Then, the mixed water is pressurized to 250 ata by means of pressure pump 13 and passes through cooler 161 to be heated by the generated in reactor 16.
The mixed water containing the PCB cools the reactor 16, while the water mixture being heated to 300.degree. C., and enters the reactor 16 through start-up heater 15. In the reactor 16, reaction occurs after a residence time necessary for decomposition of the PCB. This reaction is exothermic. In order to keep the temperature at 380.degree. C., the reactor 16 is cooled by the cooler 161.
A reacted solution discharged from the reactor 16 is cooled to a temperature of 100.degree. C. or less by cooler 17. The deposited Na.sub.2 CO.sub.3 is remelted. A pressure of the reacted solution is reduced to an atmospheric pressure by pressure reducing valve 18, and the solution is separated into CO.sub.2 and steam 20, and treated water 22 in steam separator or gas-liquid separator 21.
Exothermic reaction is carried out in the reactor 16 as expressed by the formula shown below.
PCB and solid Na.sub.2 CO.sub.3 deposited upon heating react as shown in Formula (1) so that biphenyl, CO.sub.2 and NaCl are produced. The biphenyl further reacts with aqueous hydrogen peroxide solution so that CO.sub.2 and H.sub.2 O are produced as shown in Formula (2). ##STR1##
In the reactor 16, a pipe is formed like a coil to increase a length thereof. Consequently, the residence time of the PCB in the reactor 16 is increased so that the PCB can sufficiently react, and its concentration can be reduced to the order of ppb (parts per billion).